Children?s ability to form categories is fundamental to cognitive development. The goal of this investigation is to explore how children and adults use particular cues to form spatial categories. Investigating category formation in the spatial domain is informative because space offers unique opportunities for rigorous empirical study necessary for determining how people create on-line categories. Previous research indicates that children can use temporally contiguous experience with nearby locations to form spatial groups when these groups are separated by visible boundaries. However, only older children and adults can use visible boundaries alone to form groups of locations. The proposed experiments will investigate whether children and adults can use spatiotemporal experience alone to organize locations into groups. In addition, they will explore how children and adults use spatiotemporal experience and visible boundaries to form spatial groups when these cues conflict (i.e., when visible boundaries bisect the groups of locations experienced together in time). By providing information about how children and adults use spatiotemporal experience and visible boundaries to categorize locations, this investigation represents a necessary step toward understanding developmental changes in the stability and flexibility with which children and adults create categories to meet specific contextual demands.